The Dragon and the George (Dragon #1)

Thrown from the 20th century into medieval times, Jim became a dragon: his love Angie, a damsel in distress.
First book in The Dragon Knight series.

Long Synopsis:

... he stared at rock walls leading up to a ceiling also of rock, high above his head and flickeringly lit by reddish light from a torch blazing in a wall sconce.
"Blast it, Gorbash!" roared the voice he had been trying to ignore. "Wake up! Come on, boy, we've got to get down to the main cave. They've just captured one!"
"One ... ?" Jim stammered. "One what?"
"A george! A george! WAKE UP, GORBASH!"
An enormous head with crocodile-sized jaws equipped with larger-than-crocodile-sized fangs thrust itself between Jim's eyes and the ceiling.
"I'm awake. I-" What he was seeing suddenly registered on Jim's stunned mind and he burst out involuntarily, "A dragon!"
"And just what would you expect your maternal grand-uncle to be, a sea lizard? Or are you having nightmares again? Wake up. It's Smrgol talking to you, boy. Smrgol! Come on, shake a wing and get flapping. They'll be expecting us in the main cave. Isn't every day we capture a george. Come on, now."
The fanged mouth whirled away. Blinking, Jim dropped his eyes from the vanishing apparition and caught sight of a huge tail, an armored tail with a row of sharp, bony plates running along its upper surface. It swelled larger as it approached him. It was his tail.
He held up his arms in front of him. They were enormous. Also, they were thickly scaled with bony plates like those on his tail but much smaller-and his claws needed manicuring. Squinting at the claws, Jim became aware of a long muzzle stretching down and out from where his formerly "invisible" nose had been. He licked dry lips and a long, red, forked tongue darted out briefly in the smoky air.
"Gorbash!" thundered the voice once more...